1. Field of the Invention
The present invention relates to a welding gun assembly which includes an array of transformers having secondary coils and center tap terminal plates, and electrodes connected to the secondary coils and the center tap terminal plates.
2. Description of Background Art
Heretofore, many resistance welding apparatus incorporate a transformer unit which comprises a transformer having a secondary coil across which a welding gun is connected. More specifically, first and second are connected to the terminal plate and center tap terminal plate of the transformer, and a welding gun is connected to the other ends of the conductors.
An inverter-type resistance welding apparatus has a switching device, such as a power transistor, connected to the primary side of a transformer, and a diode connected to the secondary side of the transformer. Because of the limited capacity of the power transistor or the diode, there is a certain limitation on the current which can be supplied to a welding gun connected to the transformer. If thicker plates or plated steel plates which require a relative large welding current are to be welded, then it is desirable that a plurality of transformers be connected to provide a greater welding current capacity.
Attempts have been made to design a greater-capacity, smaller-size resistance welding apparatus in which a plurality of transformers are closely arranged in a vertical or horizontal matrix, and the terminal plates and center terminal plates of each of the transformers are connected to first and second conductors that are coupled to a welding gun.
Such a welding gun with plural transformers is suitable for use with a robot for automatic welding operation, but may not easily be manually handled directly by the operator for a welding process. More specifically, the welding gun is rotatably disposed in a tubular holder which is movably suspended by a chain in a factory or shop, and the holder is operated on directly by the operator during a welding operation. However, since the transformers are arranged in a vertical or horizontal matrix, as described above, the holder which houses the transformer matrix has a large diameter. As a result, the holder is large in size, and cannot easily be handled by the operator. The efficiency of a welding process which employs the conventional welding gun with transformers is, therefore, low.